Access result of SQLite Backend Query in Custom Action

I need to process the result of a SQLite backend query in a CustomAction or Custom Function.

Is it possible to pass the result of a SQLite query to an action or function? In principle, the parameter should then be a List<SQLiteRow>, right?

I would like to return a list of a custom data type (ProjectDTO) as the result. I have to create this list from the passed SQLiteRow list.

When I want to save the custom action, I always get an error message "Unable to process parameter ..." (see screenshot)

Background:

Since the result of the BackendQuery is based on a SQL query with grouping, I cannot display the result of the BackendQuery directly in a ListView with FlutterFlow on-board tools, because rows are repeated, which does not look good. What I want to display in a ListView should look something like in Screenshot 2.

It is very urgent, because at this point my whole project could fail I would be very grateful for your help.

Here my code that can't be saved in FlutterFlow: (WHY ? )

// CustomAction gets passed a List<SQLiteRow> and returns a List<ProjectDTO>

Future<List<ProjectDTOStruct>> getDurationSums(List<SQLiteRow> projects) async {

List<ProjectDTO> resultList = [];

return resultList;
}